The present invention relates to a method of inserting weft threads through the shed of a loom by means of a stream of a fluid medium passing through a guide comb in jet weaving machines and the guide comb for performing this method.
In known jet weaving machines, the weft yarn or thread is inserted through the shed by means of an entraining fluid medium flow formed by a suitably arranged nozzle. The fluid medium flow entraining the weft yarn to be inserted is guided and directed by the guide comb, the members of which are turned at the moment of weft inserting via the lower warp thread system into the shed. Each member of the comb is provided with a weft inserting opening and has a guide profile and an unthreading gap.
The disadvantage of this so-called impulsive weft insertion arrangement resides in that, with an increasing width of the weaving machine, the range of the fluid entraining medium flow is inadequate which causes a weft insertion of inferior quality at more distant points from the nozzle. Consequently, this method of weft insertion is suitable only for weaving machines of narrow and medium widths.
There are, furthermore, known various embodiments of active weft yarn insertion methods and apparatus in which there are interposed between the members having so-called passive openings active members having active outlet conduits through which an additive fluid carrying medium is conducted, and by means of which the fluid carrying medium flow is accelerated. Among these are the arrangements shown in the U.S. Pat. Nos. to Svaty et al, 3,139,118, and Buran et al, 3,847,187. However, it has been observed that the additive fluid carrying medium in the arrangements of the prior art causes the weft yarn which is being inserted to be influenced in a negative manner by the fluid additive weft inserting medium. For example, the weft yarn frequently oscillates across the whole cross section of the weft inserting openings of the comb members. These oscillations may cause the weft yarn to enter the unthreading gap, whereby frequently weft defects are caused.
To prevent the escape of the weft thread through the unthreading gaps of the weft insertion comb members mechanical means for closing this gap have been used, e.g. a resilient diaphragm. However, such an arrangement is applicable to a limited extent only, particularly when fine weft yarns are used, or it has a very complicated construction.